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Wed, 12 Feb 2025 04:07:21 -0800 (PST) Received: from smtpclient.apple ([132.68.46.98]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab7d101ed7dsm455259866b.106.2025.02.12.04.07.19 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 12 Feb 2025 04:07:20 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.400.131.1.6\)) Subject: Re: [PATCH v10 09/12] x86/mm: enable broadcast TLB invalidation for multi-threaded processes From: Nadav Amit In-Reply-To: <20250211210823.242681-10-riel@surriel.com> Date: Wed, 12 Feb 2025 14:07:08 +0200 Cc: the arch/x86 maintainers , Linux Kernel Mailing List , Borislav Petkov , peterz@infradead.org, Dave Hansen , zhengqi.arch@bytedance.com, thomas.lendacky@amd.com, kernel-team@meta.com, "open list:MEMORY MANAGEMENT" , Andrew Morton , jackmanb@google.com, jannh@google.com, mhklinux@outlook.com, andrew.cooper3@citrix.com, Manali Shukla Content-Transfer-Encoding: quoted-printable Message-Id: <940E9420-0CD3-4C9A-AFCC-23433AF8EFA4@gmail.com> References: <20250211210823.242681-1-riel@surriel.com> <20250211210823.242681-10-riel@surriel.com> To: Rik van Riel X-Mailer: Apple Mail (2.3826.400.131.1.6) X-Rspam-User: X-Rspamd-Queue-Id: 14B9D4001A X-Stat-Signature: eg3dmx8o5w5jp9ywexhr4m337yor6rky X-Rspamd-Server: rspam03 X-HE-Tag: 1739362042-113151 X-HE-Meta: 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 a2MZmbLm 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: It all looks pretty sane to me. One small note: > On 11 Feb 2025, at 23:08, Rik van Riel wrote: >=20 > +/* > + * Check whether a process is currently active on more than = "threshold" CPUs. > + * This is a cheap estimation on whether or not it may make sense to = assign > + * a global ASID to this process, and use broadcast TLB invalidation. > + */ > +static bool mm_active_cpus_exceeds(struct mm_struct *mm, int = threshold) > +{ > + int count =3D 0; > + int cpu; > + > + /* This quick check should eliminate most single threaded = programs. */ > + if (cpumask_weight(mm_cpumask(mm)) <=3D threshold) > + return false; > + Does it make sense to first check mm.mm_users against the threshold? It = might be less cache-contended. Anyhow, for what=E2=80=99s it worth: Reviewed-by: Nadav Amit >